capercailzie vs horse of the wood

capercailzie and horse of the wood both are nouns.

Word	Noun	Adjective	Verb	Adverb
capercailzie	Yes	No	No	No
horse of the wood	Yes	No	No	No

As nouns, capercailzie and horse of the wood are synonyms defined as:

Other synonyms of capercailzie include capercaillie, Tetrao urogallus.

capercailzie (noun)	horse of the wood (noun)
large black Old World grouse	large black Old World grouse